Signaling system



yMaly`19,A 1931.11. R. K. PCTTER 1,805,596 v SIGNALING SYSTEM Filed Sept. 24, 1926 g; and amplified to a. level comparable tothatV Patented May 19, 1931ir nire raresg PATENT ferri RALPH K. POTTER., ou NEW Yeux, N. Y., Assignee. 'ro AMERICAN TELEPHONE AND e Lacasse TELEGRAPH ooiviriiiiif, ii conroniiricii en NEW Yorin sieiiALine sYsTiiM Application. le September 24, 1926. Serial No. 137,56?.

This invention relates to signaling systems,

vand particularly to such systems-in which a carrier Wave is generated at a high levelk and a band of signals is generated at a lower level of the carrieryvave.

.Vhen a. carrier Wave is generated in one circuit and voice frequency or, in general,

low frequency signals are generated in another circuit, and When the circuits are coinbined inyfor example, some suitable V'forniof modulator in conjunction with some form of filter so' that one or both side bands of the carriery Wave are producedithereby as a result of modulating and filtering action, and, furthermore, when the carrier Wave and the side bands are then .both amplified by the same amplifier, the amplifier capacity must,

in a high quality circuit. be several times that necessary to amplify the side bands alone.

In addition, undesirable noise may be in-` troduced into the amplified Wave.

In this invention7 a signaling system Will be shown and described in. which theovera-ll cn'iciency is greater than has heretoforebeen possible of attainment and the effect of circuit noisesis considerably reduced, particu-v larly during the lotv modulation period. i. e.,

the period duringA which the-level ,ofV loW frequency signals is small ascompared to the level of the carrier Wave. T he apparatus of this invention isso arranged that-,thecarrier `Wave is generated and, if'necessary,-am plilied in a circuit Whichis separate andy dis tinct from the circuit generating and amplifying the side band signals; kIn such a systeni, the requirements of the vacuum tubes employed therein are less severe andthe over,- all efficiency of the system greater -thanhas heretofore been known, by virtue of the vfact that the carrier Wave is originally generated at a high level and does not pass through several stages of amplification as do the side bands. lu addition the carrieifrequency ofk this system may be much moreV easily stabilized than in a system in Which both carrier and side band are generatedat a .highflevel While this yinvention will be `pointed out with .particularity inthe appendedclaiins,

anode and cathode.

einbodyingthe principles of this invention,

in which Fig, 3 represents a neutralizing circuit showing how ythe mutual reaction of the-carrier Wave and band of signalsV is substantially neutralized, in Which Fig. l represents a curveshowing Vthe noise characteristic of former similar signaling systenis andin which Fig. 5 represents the noise characteristic of the signaling system of this invention.A c

lReferring to F ig.r1 of the drawings, there is shown an oscillator which generates oscillations of the carrier frequency at an energy level sufficient to be directly radiated through space. This Aoscillator comprises a threeelement vacuum tube V, including a grid, an Thefcathode is heated to an electron emitting temperature by a battery 11. AA 'battery 12 supplies the space current for the vacuum tube V, through a choke coil 13. Abattery'flfl is connected to the grid of the vacuum tube '-V through a resistance 15,

vthisbattery 14 ren-dering the grid suitably negative with respect tothe cathode. The alternating current input circuit for the oscillator includes thegridfand,cathode of the `vacuum tube V, anjinductance 16, an inductance 17 and ay condenser 18.y Thealternating currentV output circuit for `the oscillator intothe `input circuitso that oscillations at thek carrier frequency are most eihciently generated. A variable condenser 21 is used in tuning theoscillation'circuit-fof the oscillator to the frequency ofthe carrier Wave. i InductancesQO and 16 Vare coupled to an kcludesthe cathode and anode of the vacuum Vtube Y, the condenser 1,9 andan inductance lli) lili] vinductance 22, which inductance is in series with another inductance 23, an antenna 24 and ground. Another inductauce 25 is coupled to inductances 1G and 2O so that part of the energy of the carrier frequency may be fed to, for example, a modulator, as Will be described mere fully hereinafter.

The Voice frequency signals may be originated by a device such as a telephone transmitter designated herein by the reference character 2G. Voice frequency signals generated by such :1 tr:V nsmitter are impressed through a transformer 2T upon a modulator, which may, for example, be of any Well known carrier suppression type, preferably of the balanced tube type as shown. The modulator comprises two three-element vacuum tubes Ml and Mg. Energy ofthe carrier frequency is transmitted from the oscillator to the modulator through coupled inductances 28 and 29, condenser 30 and coupled induetances 31 and 32.

As is well known in the art, the carrier frequency transmitted to such a modulator' is substantially suppressed, and side bands eorre'spondiner to the voice frequency signals raised in the frequency spectrum are transmitted thereby. A transformer 33 connects the output of the balanced modulator with a band filter F, which band filter transmits, for example, one side band of the carrier Wave resulting from modulation. this side band corresponding to the voice frequency signals impressed by transmitter 2G upon the balanced modulator, band lter F substantially suppressing the other side band. The band filter F suppresses, moreover, all inter-merlin lation components which are above and below the limits of the band filter. The band of signals passed by filter F is then amplified by amplier A, and is then transmitted through inductance 35 to the antenna circuit by virtue of the coupling exist-ing between inductances :l5 and 23. The circuit including the inductances 29 and 31 and the condenser 30 is a very sharply tuned circuit and serves as a means for properly adjusting the phase relations of the band of signals With respect to the carrier wave. The amplifier A raises the level of energy of the band of signals to a level approximating that of the carrier Wave, or, in general, it may be said that the amplifier A raises the energy level of the band of signals to any predetermined magnitude to produce any suitable ratio of signal energy to carrier energy.

When feeding the tubes of two or more vacuum tube circuits into a common oscillating circuit, such, for example, as an antenna circuit by means of suitable coupling of the vacuum tube circuits to the antenna circuit, the coupling may cause considerable reaction of one vacuum tube circuit upon the other. In t-he arrangement of l, the carrier output will be impressed upon the signal band output in the plate circuit of the signal band output amplifier, and will result in undesirable overloading and modulation, and similarly, the signal band output will be impressed upon the carrier output in the plate circuit of the vacuum tube supplying carrier (i. e., in, for example, the circuit of the oscillator), and will result in further undesirable overloading and lnodulation, unless suitable means are provided to prevent such interaction. To overcome such undesirable interaction and consequent intermodulation and overloading, a neutralizing circuit is provided. This neutralizing circuit consists of inductances 36 and 37 which are in series rc ationship with a condenser 38, indnctance 36 being coupled to inductance 17 and indnctance 25T being coupled to inductance The object attained by providing this neutralizing arrangement is to induce dinges in the z ysociated circuit equal and oppos e to those induced by virtue of the coupling between the carrier output, signal band output and the antenna circuit, The manner in which this neut alizing arrangement effectively suppresses undesirable inter-modulating action Will be described more particularly hereinafter in connection with Fig. 3.

In Fig. 2, a similar signaling system is shown in which the carrier Wave is generated and then amplified before being impressed upon the antenna circuit. For the sake of convenience, similar reference characters will be employed in Fig. 2 to designate parts similar to those of Fig. l. In this figure, the oscillator O generates the wave of the carrier frequency,'which oscillator may be of any well-known type. preferably of the vacuum tubetype, and may preferably be controlled as to frequency by, for example. a piezo-electric device, as is well-known in the art. This oscillator O is connected to the antenna circuit through an amplifier A, so that the level of the carrier Wave may be raised to one snitable for proper radiation by the antenna circuit. Energy of the carrier wave is also transmitted to a balanced modulator to produce a band of signals f :orrcsponding to the voice frequency signals generated by the transmitter 26, this band of signals being also amplified b v amplifier A2, separately and distinctly from the carrier wave. Due to the fact that the amplifier A, amplifies the oarrier Wave alone, the level to which the carrier Wave may be raised by the amplifier A1 is much greater than the level to which the carrier Wave might otherwise be raised, if one or both side bands of the carrier Wave were present to be simultaneously amplified thereby. mplifier A., may. as a vmatter of fact, be operated Well beyond the limits of dist-ortionless amplification and adjusted very nearly to, or even somewhat beyond, its point of as a ifrerpiency regulator.

oscillation sot'ha-t oscillator 0 may act simply in 3, a simplified diagran'i of the neutralizing arrangement is shown. The carrier output is designated by the reference character. 6l and the signal band output is designated by JdieV reference character 02. Inductances and dei simulateinductance'17 and the combination of induotances 20 and 16 of;

Vand 'Tl .simulate-inductances 22 `and 23, re-

spectii'elj.*,'oi` the antenna circuit, and resistance T2 simulates the radiation resistance ofthe antenna circuit. nductances 70 and '.71 and the resistance y@are in series relationship with the capacity 73 which represents the capacity existing between the antenna 2li of Figs. l and 2 and ground. rIlhis latterV seriescircuit simulates the antenna circuit of Figs l and 2,

TWhen the inductance. capacity and resistance of theneutralizing circuit and the inductance, capacity and resistance oi' the an# 'tenna circuit are substantiallyjequal, or,in

general, when the coupling of the Y'carrier to the .gn'al band 'source throughneutralizing circuit and through the'antenna circuit are-r suhstanti'ally equal and oprositeQthe effective emailing between, the' carrieroutput andthe -nal hand output tending to produce mutual interaction Will be'substantially Zero. y

By the arrangement of this invention, the carrier Ware and theiband of signals'corre-` sponding to voice frequency signals 'may both therefore be impressed ona common circuit Vand then radiatethrough spacesubstantially Without interaction between' the carrier Wave ,and the band of signals. .It theresistance included inl the neutralizing [arrangement (not shown) ',isfmade, for example, equal to` the total radiation resistance of'the'antennav circuit, almost ofthecarrier output and the signal band output, Will be absorbed in the nentralizingprocess. lNhen the resistance of the neutralizing*arrangement is made very small as compared to the radiation resistance ofthe antenna circuit sothatthe loss therein kis correspondingly small."the` coupling between the 'carrier output and the signalband outputmay be kadjusted. to substantially'neutralize 'mutual interaction due thecarrier Wave; but for thatV conditionjonly partial neutralization may befobtained for the signal band. "However, iyrenderi'ng the carrier eutput circuit extremeiy selective asis de- This series cirsii-able in a highly efficient generator, the system need not necessarily be'completely balanced to :prevent interaction between the carrier output and the signal jband output, because the high selectivity of the carrier circuit will operate 'effectively to obstruct the passage of signal band energy to the'carrier output circuit. Moreover,tlie selective character of the carrier output circuit Will at the same time minimize the transmission' of anycircuit disturbances suchasare caused, ior eX- am le. by ywhat are'knoivn as `ri 3 les arising P e in the plate, filament or grid'potential sources of supply for the carrier oscillator.

Fig. 4 shows the'curve approximating the relation between the circuit noise,i. e., noise, for example, due to they disturbances in the .power supply. and percentage of modulation when the cari-ier Wave and the'band of signals are bothy amplified according to present rmethods.k In this circuit, when no low fre- 'quencysignal's are modulated on the carrier Wave, the circuity noise will have a certain demt'e minimum value which is a large pei centage of the maximum and'which isV dependent upon the magnitude of circuit .dis-k lturbances and the magnitude of carrier present. Then the level ofthe llow frequency signals or modulating Wave increases, assum-` ing, ofcourse, that these signals are amplified along with the carrier Wave, the noisev will increase alinost uniformly, shown inthisfigure.

` The relation between circuit noise and percentage of modulationin 'the arrangement 'described iin connection With this invention, vis shown in Fig. 5. Vhenno low frequency signals are'modulated Vonthe carrier wam, the noise level is designated by tlie'line 100. The noise in this case is' determined Ventirely by what is present inthe oscillator which may be of the type showm'for example, in Fig. I. By the use of highly selective ircuits.

A'Which are proper for use in an unmodulated oscillatonthisnoise may bemade compara- .'tively small. LinelOl represents vthe noise vWhich visproduced bythe amplification of the band of signals. This noise'incre'ases as lthe level of the band of signals increases. y{f lhe noiseduefto the band 'of signals is at a rminimumwhen thelevel of the band is exytreinelysmall. 'Line 102 represents a line having ordinates vsubstai'itially equal to the 'ordinates of both lines 100 and'lOl. -Line 102 is,y moreover, substantially parallel to line 101. From this figure it is seen that the noise dueto the carrier Wave Will remain constant `and will be 'of comparativelyflow value, While the noise due to the amplification of the band ofsignals lWillbe in direct proportion to the percentil-geef modulation. YLine 102 will ohviouslyrepresent noise due to both the-carrier VWave andthe 'bandoffsignals somewhat f as ice The important 'difference 'between the line Y "of Fig..41and line 1020i Figf is that in'Fio.

4, the circuit noise level is comparatively high, even when no modulation is taking place, while in Fig. 5, the noise level is comparatively low when the percentage of modulation is low. With the arrangement of this invention, the circuit noise is approximately proportional to the percentage of modulation so that its interfering effect is much more nearly constant through the entire modulation range than will be ordinarily the case in systems in which the carrier and a band of signals are simultaneously amplified in common circuits.

A very important item of consideration in the case of higher power radio transmitter equipment is the saving of necessary tube capacity and power by the more efficient operation of tubes, as, for example, by operation in accordance with the principles of this in vention, described hereinabove. f

While the invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it is to be understood that the general principles of this invention may be embodied in other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. The method of signaling which consists in generating a. wave of carrier frequency, transmitting the carrier frequency Wave at a suitable energy level through space, generating voice frequency signals, producing a side band of the carrier frequency corresponding to said voice frequency signals, raising the energy level of the side-band to that of the carrier frequency, combining the side-band with the carrier frequency, and neutralizing the reaction of the energy of the carrier frequency upon that of theside-band.

2. The method of signaling which consists in generating a wave of carrier frequency, transmitting said carrier frequency wave at a suitable energy level through space, generating voice frequency signals, producing a side band of said carrier frequency corresponding to said voice frequency signals, separately amplifying said side band to an energy level substantially equal to that of the carrier frequency wave, transmitting said amplified side band through space, and neutralizing the reaction of the energy of the carrier frequency upon that of the side band before transmission. n

3. The method of signalingwhich consists in generating a carrier wave of an energy level suitable for transmission, generating low frequency signals, producing ya band of signals corresponding to said lowfrequency signals raised in the frequency spectrum, amplifying the said band of signals thus raised in the frequency spectrum to an energy level also suitable for transmission, neutralizing the reaction of the energy of the carrier wave upon that of the side-band, and transmitting through a spacial radiating me; dium both said carrier Wave and said band of signals after neutralization.

4. The method of signaling which consists in producing a high frequency carrier wave of predetermined energy level, producing voice frequency signals at a low energy level, transforming said voice frequency signals into a band of signals raised in the frequency spectrum, amplifying said band of signals raised in the frequency spectrum to said predetermined energy level, substantially neutralizing the effect of the energy of the carrier wave upon the energy of the band of signals and transmitting over a spacial radiating medium, said amplified band of signals along with said carrier wave after neutralization, thereby increasing the overall efliciency of the system.

5. A signaling system comprising means for generating a wave of carrier frequency, means for transmitting said wave of carrier frequency through space at a suitable energy level, means for generating voice frequency signals, a modulator and filter for producing a. side band of the carrier frequency wave corresponding to said voice frequency signals, and means for neutralizing the mutual reaction between said side-band and said carrier frequency wave at said transmitting means, said side band being combined with the energy of said wave of carrier frequency and being also transmitted through space by said transmitting means.

G. A signaling system comprising a generator of a carrier frequency wave, means for raising the energy level of the carrier frequency wave to a predetermined magnitude,

means for generating voice frequency signals, a modulator and filter for producing a. side band of signals corresponding to said voice frequency signals, means for amplifying said' side band to an energy level substantially equal to that of the amplified carrier wave, means including elements of inductance and capacity for neutralizing the reaction between the energy ofthe amplified side band and that of the carrier wave, and means for transmitting through a common medium the said carrier wave and said side band after each yhas been amplified.

7. A signaling system comprising a. generator of a carrier wave of an energy level suitable for transmission, a generator of low frequency signals, means for producing a band of signals corresponding to said low yfrequency signals raised in the frequency spectrum, means for amplifying said band of signals to an energy level substantially equal to that of the carrier wave, means for transmitting said carrier wave and said band of signals, and means including inductive and capacitative elements for neutralizing mutual interaction between the energy of the band of Ari.)

vLeontiae e signals and they energy of the carrier-.wavev at said transmitting means. i 8. The methodof signaling which consists in generating a carrier wave rkat an energy level requiredk for transmission, gen-` erating low frequency signals,- producing Y side band of thecarrier wavecorresponding f the energy of the carrier wave and said low frequency signals, separately amplifying said side band and the remaining portionof said carrier wave, combining said side band and said carrier wave after amplification for transmission over a common spacial radiating medium, andsubstantially neutralizing the inductive and capacitive coupling bef y tween the side band and the carrier wave energiesV tending to 'produce mutualinteraction atl the point of combination.V f

10. Themethod of signaling which consists in generating a carrier wave at a-vpre-y determined energy level, generating low free quency signals,producing`a band of signals Y corresponding to the lowifrequencysignals displaced in the frequency spectrum, sepa; rately amplifying saidrband of signals and said carrier wave so that the energy level of i said band of signals bears'a denite relation tothe energy level of thecarrier wave, comcarrier frequency, 4means for yamplifying a part VKofrrsaidcarrier frequency, means for generatingvoice frequency signals, means for combining` saidvoice frequency signals With another partf of said carrierV yfrequency in sucha Way as to produce a band of signals corresponding to said voice frequency vsignals but displaced in the frequency spectrum, means for separately amplifying said band offsignals and said carrier frequency, means for preventing mutual interaction between the energyl of said band of signals and the Venergyofsaid carrierfrequency, a commonV radiator, and means for combining and transmitting` the carrier, frequency with the band of signals Vrepresenting the ,voice frequency vsignals over said common radiatori In testimony whereof, I have signed my name, to this specification this 23rd day of September, 1926. y f n RALPH K.v POTTER,

bining said band-of signals and said carrier c wave for transmission `over acommonvme; dium, and substantially neutralizing the inductive vand capacitive coupling between the. energies of said band of signals and said car# rierwave at the point of combination.

ll. A signaling system comprising means Y for generating a carrier wave atan energy level requiredfor radiation, means for generating low frequency signals, means for modulating a fraction of the carrier wave withthe low frequency signalsto produce aside bland corresponding to Vlow frequency i signals,

c means for amplying said sidebandv to a level desirable for radiation, a common radlator,

means for preventing mutual interaction be-` tween the energy of said side-band and thel l energy of said carrier wave, and means for n combining and Ytransmitting said vcarrier wave and said side bandover said common radiator. A

- 12.*]nV aV signaling system, a generator of lui? llos

jim

lio` 

